Systems have been utilized in knitting machines for measuring unit fabric length and automatically regulating yarn feed in response thereto, for instance, to knit stockings of uniform length as disclosed in U.S. Pat. No. 2,856,764 of Cardin, or automatically to produce fabric of a predetermined density as disclosed in U.S. Pat. No. 3,225,570 of L. Mishcon. Automatic surveillance of knitting machine operation has not been utilized heretofore to optimize productivity of the knitting machine.
The formation of knitted fabric is accomplished in a knitting machine by driving needles lengthwise back and forth along slots in a needle bed causing the needles to engage and draw loops of yarn through yarn loops previously concatenated about the needles. The most commonly used arrangement for driving the needles lengthwise involves the interaction of butts on the needles or on jacks associated therewith and angled cam means such as raising or stitch cams. Indeed, even in the most sophisticated knitting machines using pattern wheels, drums or electronic devices for needle selection, such angled cams are invariably utilized for imparting the most basic stitch forming motions to the needles.
The rate at which the needles can be moved in any given knitting machine determines the productivity of the machine. It is desirable for greatest economy that the machines be operated at the maximum speed commensurate with the prescribed standard of perfection for the resulting knitted fabric. Currently, it is the practice to establish the maximum machine speed empherically and to operate the machine at a constant rate with reference to such empherical determination without regard to short term fluctuations in machine operating characteristics. As currently practiced, therefore, it is virtually a certainty that knitting machines will at times being operated at speeds higher than optimum so as to produce unnecessary fabric defects or unnecessarily severe operating conditions while at other times the machines are being operated at speeds lower than is optimum and unncessarily sacrificing productivity.